Method for multiplexing control signals and reference signals in mobile communications system

ABSTRACT

A reference signal multiplexing method for multiple mobile stations includes: grouping together control signals for the multiple mobile stations; and multiplexing reference signals corresponding to the control signals by CDM over the same bandwidth as that of grouped control signals.

This application is a continuation of U.S. application Ser. No.11/862,607 filed on Sep. 27, 2007, which is based upon and claims thebenefit of priority from Japanese Patent Application No. 2006-267765,filed on Sep. 29, 2006, the disclosure of which is incorporated hereinin its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mobile communications system and,more particularly, to a method for multiplexing control signals andreference signals (also referred to as pilot signals), a method forallocating resources, and a base station using the resource allocationmethod.

2. Description of the Related Art

In the Third Generation Partnership Project (3GPP), standardization ofLong Term Evolution (LTE), so-called 3.9G, is currently progressing. InLTE, single-carrier transmission is considered as an uplink accessscheme. It can be said that the single-carrier transmission is an accessscheme excellent for power efficiency in comparison with multi-carriertransmission, such as orthogonal frequency division multiplexing (OFDM),because the peak-to-average power ratio (PAPR) can be kept low. Hence,it can be said that the single-carrier transmission is an access schemesuitable for uplink.

FIG. 1A is a diagram showing a frame format for uplink supported by LTE,which is described in 3GPP, “TR 25.814 v7.0.0,” Section 9.1.1. In LTE,communication is performed in units of a frame (also referred to as asub-frame) of a time length of 0.5 msec. One frame includes six longblocks LB#1 to LB#6 and two short blocks SB#1 and SB#2, with a cyclicprefix (CP) added to each block, which will be described later. The timelength of a long block is set to be twice as long as that of a shortblock, and the number of subcarriers in a long block is set to be twiceas large as that in a short block. In addition, a subcarrier interval ina long block is set to be half a subcarrier interval in a short block.

Note that although two short blocks are provided here, the number ofshort blocks, which are allocated for reference signals, depends on thelength of a frame, an allowable overhead, and the like. Moreover, as forthe timings of the short blocks SB#1 and SB#2 in a frame, the structureshown in FIG. 1A is not limitative, and it suffices to determine thetimings so as to allow the reference signals to function effectively.

CAZAC (Constant Amplitude Zero Auto-Correlation) sequence is apredominant one of the sequences used for uplink reference signals. Forexample, Zadoff-Chu sequence is one type of the CAZAC sequence,represented by the following equation (see Popvic, B. M., “GeneralizedChirp-Like Polyphase Sequences with Optimum Correlation Properties,”IEEE Transactions on Information Theory, Vol. 38, No. 4 (July 1992), pp.1406-1409):

${c_{k}(n)} = \left\{ \begin{matrix}{\exp\left\lbrack {\frac{j\; 2\pi\; k}{L}\left( {\frac{n^{2}}{2} + n} \right)} \right\rbrack} & {{when}\mspace{14mu}{the}\mspace{14mu}{sequence}\mspace{14mu}{length}\mspace{14mu} L} \\\; & {{is}\mspace{14mu}{an}\mspace{14mu}{even}\mspace{14mu}{number}} \\{\exp\left\lbrack {\frac{j\; 2\pi\; k}{L}\left( {{n\frac{n + 1}{2}} + n} \right)} \right\rbrack} & {{when}\mspace{14mu}{the}\mspace{14mu}{sequence}\mspace{14mu}{length}} \\\; & {L\mspace{14mu}{is}\mspace{14mu}{an}\mspace{14mu}{odd}\mspace{14mu}{number}}\end{matrix} \right.$where n=0, 1, . . . , and L−1, and k is a sequence number, which is aninteger prime to L.

The CAZAC sequence is a sequence that makes the amplitude of a signalconstant in time and frequency domains and that allows theautocorrelation value to be zero at a phase difference of any valueother than zero. Because of the constant amplitude in time domain, PAPRcan be kept low, and because of the constant amplitude in frequencydomain as well, the CAZAC sequence is suitable for channel estimation infrequency domain. Moreover, because of the property of perfectautocorrelation, the CAZAC sequence also has the advantage of beingsuitable to detect the timing of a received signal. For these reasons,the CAZAC sequence has been attracting attention as a sequence suitablefor single-carrier transmission. However, in the case of the CAZACsequence, there is a limit to the number of sequences that can beobtained. The number of sequences depends on the sequence length. In thecase of the Zadoff-Chu sequence, the number of sequences reaches it peakwhen the sequence length L is a prime number, and the maximum number ofsequences is equivalent to (L−1).

In uplink, it is necessary that each mobile station (hereinafter, alsoexpressed as UE) transmit a reference signal. Therefore, a variety ofmethods for multiplexing reference signals of multiple UEs have beenproposed.

In 3GPP, R1-051062, Texas Instruments, “On Uplink Pilot in EUTRASC-FDMA,” October 2005, code division multiplexing (CDM) is proposed asa multiplexing method employed when the CAZAC sequence is used foruplink reference signals.

FIG. 1B is a schematic diagram for describing a method for allotting aCAZAC sequence to a reference signal of each UE. Incode-division-multiplexing of reference signals, UEs use CAZAC sequencesof the same length, and each UE is assigned a CAZAC sequence having aunique cyclic prefix added thereto as shown in FIG. 1B. If the timelength of this cyclic prefix is set to be not shorter than a maximumdelay time supposed, then the reference signals of all the UEs can beorthogonalized even in multi-path environments. This is because theautocorrelation value of a CAZAC sequence is always zero except when thephase difference is zero. Note, however, that there is a limit on thenumber of UEs that can be multiplexed by CDM with respect to referencesignal. In a current LTE system, the number of UEs that can bemultiplexed is six or so (see 3GPP, R1-060388, Motorola, “PerformanceComparison of Pilot/Reference Signal Structures for E-UTRA UplinkSC-FDMA,” February 2006).

An uplink control signal can be classified as any one of adata-dependent control signal (also referred to as a data-associatedcontrol signal), which is a control signal regarding uplink data, and adata-independent control signal (also referred to as adata-non-associated control signal), which is feedback informationregarding a downlink signal. The data-dependent control signal is asignal transmitted when uplink data is present. If a data-dependentcontrol signal is transmitted by using a resource (long block LB) fortransmitting a data signal, an essentially required reference signal(transmitted by using a short block SB) for demodulating the data signalcan also be utilized to demodulate the data-dependent control signal.

On the other hand, the data-independent control signal is a signaltransmitted as a feedback on downlink data, or the like, and is a signaltransmitted independently of an uplink data signal. Accordingly, areference signal for demodulating the data-independent control signal isrequired, and the problem of how to allocate a resource for thereference signal arises.

In the foregoing, data-dependent and data-independent control signalshave been described with respect to uplink control signal. However, withrespect to downlink control signal as well, it can be said that acontrol signal transmitted when downlink data is present (adata-dependent control signal, which is a control signal regardingdownlink data) is a downlink data-dependent control signal, and that asignal transmitted independently of a downlink data signal (adata-independent control signal, which is feedback information regardingan uplink signal) is a downlink data-independent control signal.Hereinafter, to simplify expression, it is assumed that a “controlsignal” indicates a “data-independent control signal.”

Examples of control information, which is contained in an uplinkdata-independent control signal, at least includeAcknowledgment/Negative Acknowledgment (hereinafter, expressed asAck/Nack) indicating whether or not downlink information has beenreceived without errors, channel quality indication information (channelquality indicator: hereinafter, expressed as CQI) indicating the stateof a downlink channel, a combination of these, and the like. It isdesirable that Ack/Nack be transmitted at every transmission timeinterval (hereinafter, expressed as TTI). However, with the transmissionoverhead being considered, it is not always necessary to transmit CQI atevery TTI. For this reason, there are some occasions when the frequencyof transmission of Ack/Nack differs from the frequency of transmissionof CQI. Accordingly, within a TTI, UEs transmitting three types ofcontrol signals may coexist: a UE transmitting Ack/Nack only, a UEtransmitting CQI only, and a UE transmitting both of Ack/Nack and CQI.Incidentally, TTI is a time interval equivalent to a set of multipleblocks (also referred to as a transport block set) transported at a timebetween the physical and MAC layers.

However, the amount of information of Ack/Nack is smaller than that ofCQI. It is possible to make transmission bandwidths of theabove-mentioned three types of control signals constant by changing therate of encoding, or transmitting dummy bits. However, if thesetransmission bandwidths are made constant, waste occurs with a resource(transmission bandwidth) used to transmit a signal having a small amountof information. To avoid the occurrence of such waste of resource,frequency resources (transmission bandwidths) allocated to transmit therespective control signals are, in general, different transmissionbandwidths of three types.

In addition, the transmission made by a UE simultaneously transmittingAck/Nack and CQI is multi-carrier transmission if corresponding controlresources are mapped in uncontiguous frequency bands, resulting inincreased PAPR. Accordingly, in order for a UE simultaneouslytransmitting Ack/Nack and CQI to make single-carrier transmission,resources in adjacent frequency bands need to be allocated to the UE,and these signals need to be processed together. This will be describedmore specifically with reference to FIGS. 2A and 2B.

FIG. 2A is a diagram showing frequency resource allocation in the caseof multi-carrier transmission of control signals, and FIG. 2B is adiagram showing frequency resource allocation in the case ofsingle-carrier transmission of control signals. Referring to FIG. 2A,when control resources in uncontiguous frequency bands F1 and F2 areallocated to a UE which simultaneously transmits Ack/Nack and CQI, theUE cannot perform single-carrier transmission. Accordingly, PAPR isincreased as described above.

Therefore, the frequency resources for transmitting Ack/Nack and CQI aremapped into a combined band of adjacent frequency bands F3 and F4 asshown in FIG. 2B, whereby these bands can be handled as a single band,enabling single-carrier transmission.

FIG. 3 is a diagram showing an example of the allocation of resourcesfor control and reference signals. Here, shown is the case, as anexample, where control signals in a long block LB#1 and referencesignals in a short block SB#1 are time-division-multiplexed (TDM).Incidentally, a numeral applied to each control or reference signal inthe drawing represents a UE's number (the same goes for the otherdrawings.)

As to the control signals regarding downlink data signals, there arethree types of UEs coexisting, each transmitting Ack/Nack only, CQIonly, or both of Ack/Nack and CQI, as described above. Here, UEs 1 and 6each transmit both of Ack/Nack and CQI, UEs 2 and 3 each transmitAck/Nack only, and UEs 4 and 5 each transmit CQI only.

However, according to a conventional resource allocation method, areference signal is allocated a reference resource in the same bandwidthwhich a control signal to be demodulated is transmitted in. That is,reference resources each corresponding to three types of transmissionbandwidths are to be allocated. Therefore, a reference signal fordemodulating Ack/Nack, which has a small amount of information and hencea small transmission bandwidth, also has a reduced transmissionbandwidth. Since the length of the CAZAC sequence, which is used forreference signals, depends on the transmission bandwidth as describedabove, the number of usable reference signal sequences (CAZAC sequences)decreases when Ack/Nack only is transmitted.

However, the number of reference signal sequences is an important factorto the cell designing in a cellular system composed of multiple cells.The reason is that the use of the same reference signal sequence byadjacent cells leads to increased interference between the cells, and toavoid this, adjacent cells need to use different reference signalsequences. According to the conventional resource allocation method, asdescribed above, if a transmission bandwidth is small as in the case ofAck/Nack, the length of the usable CAZAC sequence is short. Therefore,the problem arises that there occurs a shortage of the sequences to beused for reference signals at the time of transmission.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a multiplexing methodand a resource allocation method that can ensure the number of codesequences for reference signals for control signal demodulation.

According to the present invention, a method for multiplexing referencesignals for a plurality of mobile stations, comprising: groupingtogether control signals for the plurality of mobile stations; andmultiplexing reference signals corresponding to the control signals byCDM (code-division multiplexing) over a same bandwidth as that ofgrouped control signals.

According to the present invention, reference signals of multiple UEsare code-division-multiplexed over the same bandwidth as that of groupedcontrol signals. Thereby, the number of code sequences for referencesignals used for control signal demodulation can be ensured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram showing a frame format for uplink supported by LTE,described in 3GPP, “TR 25.814 v7.0.0,” Section 9.1.1.

FIG. 1B is a schematic diagram for describing a method for allotting aCAZAC sequence to a reference signal of each UE.

FIG. 2A is a diagram showing frequency resource allocation in the caseof multi-carrier transmission of control signals.

FIG. 2B is a diagram showing frequency resource allocation in the caseof single-carrier transmission of control signals.

FIG. 3 is a diagram showing an example of the allocation of resourcesfor control and reference signals.

FIG. 4 is a block diagram showing a schematic configuration of a basestation to implement the present invention.

FIG. 5 is a block diagram showing a schematic configuration of a mobilestation (UE) to implement the present invention.

FIG. 6A is a schematic diagram showing an example of the grouping ofcontrol resources according to the present invention.

FIG. 6B is a schematic diagram showing the generalized grouping ofcontrol resources according to the present invention.

FIG. 7 is a flowchart showing an example of a resource allocation methodaccording to the present invention.

FIGS. 8A to 8C are schematic diagrams showing schemes for multiplexingcontrol and reference signals according to first to third exemplaryembodiments of the present invention, respectively.

FIG. 9 is a diagram showing an example of the allocation of resourcesfor control and reference signals according to the first exemplaryembodiment of the present invention.

FIG. 10 is a diagram showing another example of the allocation ofresources for control and reference signals according to the firstexemplary embodiment of the present invention.

FIG. 11 is a diagram showing an example of the allocation of resourcesfor control and reference signals according to the second exemplaryembodiment of the present invention.

FIG. 12 is a diagram showing another example of the allocation ofresources for control and reference signals according to the secondexemplary embodiment of the present invention.

FIG. 13 is a diagram showing an example of the allocation of resourcesfor control and reference signals according to the third exemplaryembodiment of the present invention.

FIG. 14 is a diagram showing another example of the allocation ofresources for control and reference signals according to the thirdexemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 1. System

FIG. 4 is a block diagram showing a schematic configuration of a basestation to implement the present invention. A base station 100 includesa radio communication section 101, which demodulates an uplink controlsignal and/or uplink data signal received from mobile stations (UEs) inaccordance with corresponding reference signals similarly received, andwhich outputs the control signals to a control information extractionsection 102. Here, a “resource” means a frequency-time region specifiedby the frequency band and time period required to transmit a signal.Moreover, a resource to be allocated to a control signal is referred toas a control resource, and a resource to be allocated to a referencesignal is referred to as a reference resource.

The control information extraction section 102 extracts information,such as a request for uplink resource allocation from a mobile stationhere, and outputs the information to a scheduler 103. The scheduler 103includes a resource allocation section 104 that executes controlresource allocation and reference resource allocation, which will bedescribed later. Additionally, although not shown in the drawing, thebase station 100 also includes a memory area for storing informationabout past resource allocation, another scheduler that executes downlinkresource allocation, and a CQI measurement section that measures CQIbased on an uplink reference signal received by the radio communicationsection 101. The resource allocation section 104 acquires theinformation about past resource allocation held in the memory area,information about the presence or absence of downlink data to be sent toeach mobile station from the scheduler that executes downlink resourceallocation, CQI of each mobile station from the CQI measurement section,and the like. Based on these pieces of information, the resourceallocation section 104 generates resource allocation informationincluding resource allocation for each mobile station and itsmultiplexing scheme, and outputs the resource allocation information toa control signal generation section 106. Here, the multiplexing schemeis information indicative of any one of localized frequency divisionmultiplexing (LFDM) and distributed frequency division multiplexing(DFDM), as a method of multiplexing control signals.

The control signal generation section 106 generates a control signalcontaining the resource allocation information for each mobile stationand transmits the control signal to each mobile station through theradio communication section 101. Here, it is assumed that the resourceallocation information includes information about which frequency band(hereinafter, also referred to as frequency resource) at which time (orin which block: hereinafter, also referred to as time resource) isallocated to which mobile station.

Incidentally, the base station 100 is provided with a control section105 that controls the operations of the base station. Resourcemanagement by the scheduler 103 is performed under the control of thecontrol section 105. In general, the control section 105 performsvarious controls, such as resource allocation control, by executingcontrol programs on a program-controlled processor such as a CPU. Thescheduler 103 and resource allocation section 104 can also beimplemented by executing respective programs on the sameprogram-controlled processor or on a separate program-controlledprocessor.

FIG. 5 is a block diagram showing a schematic configuration of a mobilestation (UE) to implement the present invention. A mobile station 200includes a radio communication section 201, which demodulates a downlinkcontrol signal and/or downlink data signal received from the basestation 100 by using corresponding reference signals similarly received,and which outputs the control signal to a control information extractionsection 202. The control information extraction section 202 extractsresource allocation information and outputs it to a control section 203.

First, in accordance with the resource allocation information, thecontrol section 203 individually controls a data generation section 204,a CQI generation section 205, an Ack/Nack generation section 206, aCAZAC sequence generation section 207, and a cyclic shift section 208 sothat these sections generate respective signals at respective timingsaccording to the time resource allocation information. Further, thecontrol section 203 individually controls a subcarrier mapping section210-1 for control and data signals and a subcarrier mapping section210-2 for reference signals.

The data signal and/or control signal generated by the data generationsection 204, CQI generation section 205, and/or Ack/Nack generationsection 206 are transformed into frequency-domain signals by a discreteFourier transform (DFT) section 209-1, and the respectivefrequency-component signals in the frequency domain are outputted to thesubcarrier mapping section 210-1. The subcarrier mapping section 210-1determines, in accordance with the frequency resource allocationinformation from the control section 203, which subcarriers to be usedto transmit the signals inputted from the DFT section 209-1 (subcarriermapping). For example, in accordance with the frequency resourceallocation information from the control section 203, the subcarriermapping section 210-1 can perform subcarrier mapping by means oflocalized frequency division multiplexing (LFDM) using contiguoussubcarriers, or subcarrier mapping by means of distributed frequencydivision multiplexing (DFDM) using subcarriers spaced at fixedintervals.

The frequency-domain signals subjected to subcarrier mapping by thesubcarrier mapping section 210-1 are transformed into time-domainsignals by an inverse fast Fourier transform (IFFT) section 211-1 beforea cyclic prefix adding section 212-1 adds cyclic prefixes (CPs) to thetime-domain signals.

As for the reference signal, the CAZAC sequence generation section 207generates a CAZAC sequence as a reference signal in accordance with theresource allocation information from the control section 203. The cyclicshift section 208 cyclic-shifts the CAZAC sequence by an amount of timelength unique to each mobile station as described with reference to FIG.1B and outputs the resultant CAZAC sequences to a DFT section 209-2. Theoperations of the DFT section 209-2, the subcarrier mapping section210-2, an IFFT section 211-2, and a cyclic prefix adding section 212-2are similar to those in the case of the data signal and/or controlsignal described above, and therefore a description thereof will beomitted.

The data signal and/or control signal thus outputted from the cyclicprefix adding section 212-1 and the reference signal thus outputted fromthe cyclic prefix adding section 212-2 are time-division-multiplexed(TDM) by a multiplexer section (MUX) 213, and the multiplex signal istransmitted to the base station 100 through the radio communicationsection 201.

In the system configuration described above, the allocation of resourcesand the multiplexing of control and reference signals according toembodiments of the present invention are performed, which will bedescribed next in detail.

2. Resource Allocation by Grouping Together

A basic concept of the present invention is that reference signals ofmultiple mobile stations (UEs) are code-division-multiplexed (CDM) in abandwidth that is obtained by grouping together the transmissionbandwidths of control signals to be transmitted by the multiple mobilestations. Hereinafter, such a bandwidth obtained by the grouping isreferred to as a total bandwidth. An example of the grouping of controlsignals will be described.

FIG. 6A is a schematic diagram showing an example of the grouping ofcontrol resources according to the present invention, and FIG. 6B is aschematic diagram showing the generalized grouping of control resourcesaccording to the present invention. Here, it is assumed that grouping isperformed so that I groups are formed at the maximum, wherein each groupi is a group of control resources that meets limiting conditionsundermentioned.

For simplicity, it is assumed that, as shown in FIG. 6A, there arepieces of control information C₁ to C₄ having different transmissionbandwidths to be transmitted by UEs 1 to 8. Here, the “pieces of controlinformation having different transmission bandwidths” are those whichhave different amounts of information and which are individuallycontained in control signals to be transmitted by UEs. In this case, theresource allocation section 104 of a base station, while taking accountof the bandwidth of the control information of each mobile station,forms a group i such that the total bandwidth is not smaller than atarget bandwidth (hereinafter, referred to as a target L_(TH), which isexpressed in the length of a corresponding sequence) and that a limitingcondition regarding the total number of multiplexed UEs is satisfied.The resource allocation section 104 then carries out resource allocationfor the UEs that transmit the pieces of control information grouped.

For example, GROUP 1 is formed by grouping together the pieces ofcontrol information C₁ of the UEs 1, 3, and 4 and the pieces of controlinformation C₂ of the UEs 2 and 5 so that the total bandwidth of thesepieces of control information is not smaller than a bandwidth equivalentto the target L_(TH) and that the limiting condition regarding the totalnumber of multiplexed UEs is satisfied. Incidentally, in GROUP 1 asshown in FIG. 6A, the numerals under “C₁” and “C₂,” which representcontrol information, indicate corresponding UEs.

Based on the thus formed GROUP 1, one frequency band is made in whichthe bands of the control signals are collected. The pieces of controlinformation of the other UEs that are not included in GROUP 1 aresubjected to grouping similarly, to be included in any of the next GROUP2 and subsequent GROUPs. Additionally, if a single piece of controlinformation meets the condition that the total bandwidth is not smallerthan the target L_(TH), a group may be composed of this piece of controlinformation only. In this example, GROUP i in FIG. 6A includes only thecontrol information C₄ of the UE 8.

Another example of the method for grouping such multiple pieces ofcontrol information having difference transmission bandwidths will bedescribed hereafter. Here, it is assumed that a setting is made suchthat, as shown in FIG. 6B, each GROUP i can include multiple types ofcontrol information C₁, C₂, . . . , C_(J) having different transmissionbandwidths, in maximum numbers of R₁, R₂, . . . , R_(J), respectively,so that the condition regarding the total bandwidth and the limitingcondition regarding the total number of multiplexed UEs are bothsatisfied. In the case of this example, the numbers of control resourcesto be allocated for the respective types of control information C_(j) ineach GROUP i, R_(j), are fixed at the same number. Here, “J” is thenumber of types of control information having different amounts ofinformation that are individually contained in control signals to betransmitted by UEs. Assuming that there are two types of controlinformation, “Ack/Nack” and “CQI”, as in the example described earlier,control information that is selected and transmitted by each UE is ofany one of the following three types: “Ack/Nack,” “CQI,” and“Ack/Nack+CQI.” Since these three (J=3) types of control informationhave different amounts of information, they correspond to pieces ofcontrol information C₁ to C₃ having difference transmission bandwidths.Accordingly, R₁ to R₃ are upper limits, respectively, for the number ofpieces of control information C₁, the number of pieces of controlinformation C₂, and the number of pieces of control information C₃ whenthey are mapped to each GROUP i.

As an example, it is assumed that, with J=3, a setting is made such thatR₁=3, R₂=2, and R₃=1, for groups 1 to I. UEs are mapped to GROUPs 1 toI, in order of the types of control information as in FIG. 6A(specifically, in the order: C₁, C₂, and C₃). First, the UEs 1, 3, 4,and 7 transmitting control information C₁ are mapped to GROUPs, startingfrom GROUP 1. Since R₁=3, the UEs 1, 3, and 4 are mapped to GROUP 1, andthe UE 7 is mapped to the next GROUP 2. In this manner, with respect toevery type of control information, the UEs can be sequentially mapped toGROUPs.

Thus, control signals for multiple UEs are grouped so that the totalbandwidth of the grouped control signals is not smaller than a fixedtransmission bandwidth. Based on this total bandwidth of the groupedcontrol signals, corresponding reference signals are multiplexed by CDM.

FIG. 7 is a flowchart showing an example of a resource allocation methodaccording to the present invention. First, the resource allocationsection 104 of a base station sets a target L_(TH), which is a CAZACsequence length (ST301). The target L_(TH) can be obtained based on thenumber of sequences required in a system. For example, if twelve CAZACsequences are required, the target L_(TH) is 13. If nine CAZAC sequencesare required, the target L_(TH) is 11.

Subsequently, the resource allocation section 104 groups togetherresources to be allocated for multiple types of control informationC_(j) (1≦j≦J) so that the following two conditions are both satisfied(ST302).

Condition 1) The total multiplex bandwidth of grouped control signals isnot smaller than the target L_(TH).

Condition 2) The total number of multiplexed UEs is not larger than themaximum number of reference signals that can be multiplexed.

Here, it is assumed that “I” is the number of groups formed, and thateach group includes R_(j) control resources for transmitting controlinformation C_(j) (see FIG. 6B).

Next, j is initialized to 1 (ST303), and the control resource fortransmission of control information C_(j) (here, control information C₁)is allocated to UEs, in each group (ST304). Taking the case describedwith reference to FIG. 6B as an example, the control resources for thecontrol information C_(j) are allocated to a maximum of (R_(j)×I) UEs inthis step ST304. The processing in the step ST304 is repeated while j isincremented each time, until j reaches a maximum value of J (ST305,ST306). In this manner, the pieces of control information of themultiple UEs are grouped and mapped to the control resources in acollective frequency band.

Subsequently, the resource allocation section 104 determines whether ornot an unallocated control resource remains (ST307). When no unallocatedcontrol resource remains (ST307: NO), the processing is terminated. Whenthere remains an unallocated control resource (ST307: YES), the resourceallocation section 104 determines whether or not there is a UE to whicha resource could not be allocated in the above-described processingsteps ST304 to ST306 (ST308). When such a UE waiting for resourceallocation is present (ST308: YES), the resource allocation section 104assigns a degree of priority k (hereinafter, simply referred to as apriority k) to that UE in accordance with undermentioned criteria(ST309), and then carries out resource allocation control in accordancewith the priority as described below.

The priority to be assigned to a UE is determined based on the type ofcontrol information, the length of time for which the UE has beenwaiting, and the like. For example, higher priorities are assigned toUEs such as a UE that is to transmit information more susceptible todelay, such as Ack/Nack, and a UE that has been waiting for a longertime. Incidentally, it is assumed that “1” is the highest priority,followed by 2, 3, . . . , and K in descending order of priority.

First, the priority k is initialized to 1 (ST310). When k (here, 1) isnot larger than K (ST311: YES), then it is determined whether or notthere is a UE waiting for resource allocation with the currentlydesignated priority k (here, 1) (ST312). When such a UE is not presentin the step ST312 (ST312: NO), the priority k is incremented (ST313),and then, if k is not larger than K, it is determined whether or not aUE with the new priority k is present (ST312). When such a UE is presentin the step ST312 (ST312: YES), it is determined whether or not aresource can be allocated to the UE with the currently designatedpriority k (ST314). If allocation is impossible (ST314: NO), the controlgoes back to the step ST313. If allocation is possible (ST314: YES), aresource is allocated to the UE with the currently designated priority k(ST315), and then the control returns to the step ST313. In this manner,the steps ST311 to ST315 are repeated for every priority. When thepriority k exceeds K (ST311: NO), the processing is terminated.

3. Multiplexing Scheme

Basic concepts of a multiplexing scheme according to the presentinvention are as follows.

(1) Control signals for multiple UEs are grouped together and thenmultiplexed by frequency division multiplexing (FDM).

(2) Reference signals are multiplexed by code division multiplexing(CDM) over the same bandwidth as that grouped control signals formultiple UEs.

Since the reference signals are multiplexed by CDM over the samebandwidth as the total bandwidth of the grouped control signals formultiple UEs, the number of usable CAZAC sequences can be increased.

In accordance with the above-described grouping of control signals, theresource allocation section 104 multiplexes control signals andreference signals by using any one of multiplexing schemes describedbelow.

FIGS. 8A to 8C are schematic diagrams showing schemes for multiplexingcontrol and reference signals according to first to third exemplaryembodiments of the present invention, respectively.

Referring to FIG. 8A, according to a first exemplary embodiment of thepresent invention, grouped control signals for multiple UEs aremultiplexed by distributed FDM (DFDM), and corresponding referencesignals are multiplexed by CDM or by a hybrid of FDM and CDM. In thiscase, the hybrid of FDM and CDM is a scheme by which reference signalsof those UEs over the same bandwidth for transmission arecode-division-multiplexed and reference signals of those UEs overdifferent bandwidths for transmission are frequency-division-multiplexed(DFDM). Specific examples will be described later.

Referring to FIG. 8B, according to a second exemplary embodiment of thepresent invention, grouped control signals for multiple UEs aremultiplexed by localized FDM (LFDM), and corresponding reference signalsare multiplexed by CDM or by the hybrid of FDM and CDM.

Referring to FIG. 8C, according to a third exemplary embodiment of thepresent invention, grouped control signals for multiple UEs aremultiplexed by LFDM, and then, among groups of such grouped controlsignals, control signals in those groups over the same bandwidth aremultiplexed by DFDM. Corresponding reference signals are multiplexed byCDM or by the hybrid of FDM and CDM.

Hereinafter, assuming that there are two types of control signals havingdifferent amounts of information (Ack/Nack and CQI), a description willbe given, as an example, of the case where there are three types ofbandwidths: a bandwidth for transmitting Ack/Nack only, a bandwidth fortransmitting CQI only, and a bandwidth for transmitting both of Ack/Nackand CQI.

4. First Exemplary Embodiment

According to the first exemplary embodiment of the present invention,resource allocation is performed by a base station such that amongcontrol signals for multiple UEs, control signals having the samebandwidth are multiplexed by DFDM, and reference signals for those UEscorresponding to the DFDM control signals are multiplexed by CDM overthe total bandwidth of the DFDM control signals.

Specifically, the resource allocation section 104 acquires informationabout past resource allocation, information about the presence orabsence of downlink data to be sent to each UE, which is acquired fromthe scheduler performing downlink resource allocation, and the like.Based on these pieces of information, the resource allocation section104 selects from among multiple types of control information havingdifferent amounts of information (here, “Ack/Nack” and “CQI”) one typeor multiple types of control information (here, any one or both of“Ack/Nack” and “CQI”) for each UE, and allocates each UE a bandwidthaccording to the amount of the selected information. The resourceallocation section 104 then generates resource allocation informationindicating the allocated bandwidths and also indicating that among theUEs allocated the multiple types of bandwidths, control signals forM_(i) UEs (1≦M_(i)≦N, 1≦i≦I, M₁+M₂+ . . . +M_(I)=N) that are allocatedthe same transmission bandwidth are grouped together to form I groupsand are multiplexed by DFDM, and that reference signals for the M_(i)UEs in each of the I groups are multiplexed by CDM in a referenceresource having the same bandwidth as the total bandwidth of the groupedcontrol signals included in the group. The resource allocationinformation is information as shown in FIG. 10 for example, which willbe described later.

4.1) Example 1

FIG. 9 is a diagram showing an example of the allocation of resourcesfor control and reference signals according to the first exemplaryembodiment of the present invention. Here, it is assumed that controland reference signals are multiplexed by time division multiplexing(TDM), and that in each sub-frame, data and control signals aretransmitted in long blocks (LB) and reference signals are transmitted inshort blocks (SB), as shown in FIG. 1A for example.

Specifically, referring to FIG. 9, UEs 1 and 6 are those transmittingboth of Ack/Nack and CQI and are multiplexed by DFDM with a repetitionfactor of 2 over a bandwidth that is twice as wide as a bandwidth fortransmitting Ack/Nack and CQI. With respect to reference signals for theUEs 1 and 6, the two UEs are multiplexed by CDM over the bandwidth thatis twice as wide as the bandwidth for transmitting Ack/Nack and CQI.

UEs 2 and 3 are those transmitting Ack/Nack only and are multiplexed byDFDM with a repetition factor of 2 over a bandwidth that is twice aswide as a bandwidth for transmitting Ack/Nack. With respect to referencesignals for the UEs 2 and 3, the two UEs are multiplexed by CDM over thebandwidth that is twice as wide as the bandwidth for transmittingAck/Nack.

Similarly, UEs 4 and 5 are those transmitting CQI only and aremultiplexed by DFDM with a repetition factor of 2 over a bandwidth thatis twice as wide as a bandwidth for transmitting CQI. With respect toreference signals for the UEs 4 and 5, the two UEs are multiplexed byCDM over the bandwidth that is twice as wide as the bandwidth fortransmitting CQI.

According to the resource allocation of the present example, since thebandwidth for each reference signal is doubled in comparison with thoseaccording to the related arts as shown in FIG. 3, the number of CAZACsequences can be made approximately twice as large. Incidentally, in thecase where n UEs are multiplexed by CDM, the number of CAZAC sequencescan be made approximately n times larger because the bandwidth of eachreference signal is n times wider.

Note that although control and data signals are multiplexed by TDM inthe present example, the resource allocation of the present example issimilarly applicable in the case where control and data signals aremultiplexed by FDM.

4.2) Example 2

FIG. 10 is a diagram showing another example of the allocation ofresources for control and reference signals according to the firstexemplary embodiment of the present invention. Here, it is assumed thatin each sub-frame, control signals are transmitted in a long block LB#1,reference signals are transmitted in short blocks SB#1 and SB#2, anddata signals are transmitted in long blocks LB#2 to LB#6, as shown inthe LTE's uplink frame format in FIG. 3.

When a data signal is transmitted in long blocks LB#2 to LB#6, areference signal for demodulating the data signal is transmitted in eachof short blocks SB#1 and SB#2. In the present example, in the shortblock SB#1, a reference signal for a UE 7, which transmits data, ismultiplexed by DFDM with, for example, reference signals for controlsignals for UEs 1 and 6 that are multiplexed by CDM (the hybrid of FDMand CDM). In the short block SB#2, a reference signal for the UE7 ismultiplexed by DFDM with a reference signal for CQI measurement of a UE8. Incidentally, in FIG. 10, UE's numbers shown with “/” between themindicate that these UEs are multiplexed by CDM. The same goes for theother drawings.

Note that although control and data signals are multiplexed by TDM inthe present example, the resource allocation of the present example issimilarly applicable in the case where control and data signals aremultiplexed by FDM.

4.3) Advantages

According to the first exemplary embodiment of the present invention,control signals having the same bandwidth are multiplexed by DFDM, andcorresponding reference signals are multiplexed by CDM over thebandwidth where the control signals are multiplexed by DFDM, and thentransmitted. Thereby, the reference signal sequence length is madelonger as many times as the number of the UEs multiplexed by CDM.Accordingly, the number of CAZAC sequences usable as reference signalscan be made larger approximately as many times as the number of the UEsmultiplexed by CDM.

5. Second Exemplary Embodiment

According to the second exemplary embodiment of the present invention,reference signals for multiple UEs whose control signals are multiplexedby LFDM, are multiplexed by CDM.

In other words, according to the second exemplary embodiment of thepresent invention, among multiple types of control information havingdifferent amounts of information (here, “Ack/Nack” and “CQI”), one typeor multiple types of control information (here, any one or both of“Ack/Nack” and “CQI”) is selected for each UE; a bandwidth according tothe amount of the selected information is allocated to each UE; controlsignals for M_(i) UEs (1≦M_(i)≦N, 1≦i≦I, M₁+M₂+ . . . +M_(I)=N) aregrouped together to form I groups and are multiplexed by LFDM; referencesignals for the M_(i) UEs in each of the I groups are multiplexed by CDMin a reference resource having the same bandwidth as the total bandwidthof the grouped control signals included in the group.

In the present embodiment, there coexist UEs transmitting threedifferent types of control signals: those transmitting Ack/Nack only,those transmitting CQI only, and those transmitting both of Ack/Nack andCQI. One channel of Ack/Nack and one channel of CQI are grouped. A UEtransmitting both of Ack/Nack and CQI is allocated an entire bandwidthobtained by this grouping. A UE transmitting Ack/Nack only and a UEtransmitting CQI only share the bandwidth obtained by this grouping andare multiplexed by LFDM. Corresponding reference signals are multiplexedby CDM over the bandwidth obtained by this grouping. Accordingly, incomparison with the methods according to the related arts, it ispossible to increase the number of usable CAZAC sequences.

5.1) Example 3

FIG. 11 is a diagram showing an example of the allocation of resourcesfor control and reference signals according to the second exemplaryembodiment of the present invention. Here, it is assumed that controland reference signals are multiplexed by time division multiplexing(TDM), and that in each sub-frame, data and control signals aretransmitted in long blocks (LB) and reference signals are transmitted inshort blocks (SB), as shown in FIG. 1A for example.

In the present example, a bandwidth used when one channel of Ack/Nackand one channel of CQI are transmitted is supposed to be a unitbandwidth used to multiplex reference signals by CDM. Specifically, a UEtransmitting Ack/Nack only and a UE transmitting CQI only aremultiplexed by LFDM over the total bandwidth of Ack/Nack and CQI, and aUE transmitting both of Ack/Nack and CQI is independently allocated thetotal bandwidth of Ack/Nack and CQI.

More specifically, referring to FIG. 11, UEs 1 and 6 are thosetransmitting both of Ack/Nack and CQI. Each of their control signals istransmitted by single-carrier transmission in a continuous band as isdone conventionally, and their corresponding reference signals aretransmitted over the bandwidths corresponding to Ack/Nack and CQI,respectively. In this case, the reference signal for demodulating thecontrol signal does not particularly need to be multiplexed by CDM.

On the other hand, a UE 2, which transmits Ack/Nack only, and a UE 4,which transmits CQI only, are multiplexed by LFDM in adjacent bands, andreference signals of the UEs 2 and 4 are multiplexed by CDM over thetotal bandwidth of Ack/Nack and CQI. For a UE 3, which transmitsAck/Nack only, and a UE 5, which transmits CQI only, multiplexing isperformed as in the case of the UEs 2 and 4.

According to the present example, for the UEs 2 and 3, which transmitAck/Nack only, the reference signals are transmitted using the totalbandwidth of Ack/Nack and CQI. Therefore, unlike the examples of therelated arts, it is possible to avoid a reduction in the CAZAC sequencelength.

Note that although control and data signals are multiplexed by TDM inthe present example, the resource allocation of the present example issimilarly applicable in the case where control and data signals aremultiplexed by FDM.

5.2) Example 4

FIG. 12 is a diagram showing another example of the allocation ofresources for control and reference signals according to the secondexemplary embodiment of the present invention. Here, it is assumed thatin each sub-frame, Ack/Nack and/or CQI, which are control signals, aretransmitted in a long block LB#1, reference signals are transmitted inshort blocks SB#1 and SB#2, and data signals are transmitted in longblocks LB#2 to LB#6, as shown in the LTE's uplink frame format in FIG.3.

When a data signal is transmitted in long blocks LB#2 to LB#6, areference signal for demodulating the data signal is transmitted in eachof short blocks SB#1 and SB#2. According to the present example, in theshort block SB#1, a reference signal of a UE 7, which transmits data, ismultiplexed by DFDM with, for example, reference signals for controlsignals for UEs 2 and 4 that are multiplexed by CDM (the hybrid of FDMand CDM). In the short block SB#2, a reference signal of the UE 7 ismultiplexed by DFDM with a reference signal for CQI measurement of a UE9.

Reference signals of UEs 1 to 6, which transmit control signals only,are multiplexed as described earlier. Specifically, a reference signalof the UE 1, which transmits both of Ack/Nack and CQI, is transmittedover a total bandwidth corresponding to both Ack/Nack and CQI, withoutbeing code-division-multiplexed. The UE 2, which transmits Ack/Nackonly, and the UE 4, which transmits CQI only, are multiplexed by LFDM inadjacent bands, and reference signals of the UEs 2 and 4 are multiplexedby CDM over the total bandwidth corresponding to both Ack/Nack and CQI.The UE 3, which transmits Ack/Nack only, and the UE 5, which transmitsCQI only, are multiplexed similarly to the UEs 2 and 4.

Note that although control and data signals are multiplexed by TDM inthe present example, the resource allocation of the present example issimilarly applicable in the case where control and data signals aremultiplexed by FDM.

5.3) Advantages

According to the second exemplary embodiment of the present invention,reference signals of multiple UEs whose control signals are multiplexedby LFDM are multiplexed by CDM over the total bandwidth of the LFDMcontrol signals, whereby it is possible to avoid a reduction in theCAZAC sequence length. Additionally, the CAZAC sequence length can bemade constant.

6. Third Exemplary Embodiment

According to the third exemplary embodiment of the present invention,control signals for multiple UEs are grouped and multiplexed by LFDM;among thus formed groups, one or more control signals in those groupshaving the same bandwidth are multiplexed by DFDM; reference signals ofthe UEs whose control signals are multiplexed by DFDM are multiplexed byCDM over the total bandwidth of the DFDM control signals.

In other words, among multiple types of control information havingdifferent amounts of information (here, “Ack/Nack” and “CQI”), one typeor multiple types of control information (here, any one or both of“Ack/Nack” and “CQI”) is selected for each UE; a bandwidth according tothe amount of the selected information is allocated to each UE; controlsignals for M_(i) UEs (1≦M_(i)≦N, 1≦i≦I, M₁+M₂+ . . . +M_(I)=N) aremultiplexed by LFDM, regardless of the respective bandwidths allocatedto the UEs. Among I groups thus formed, G groups having the samebandwidth are selected; control signals for those UEs belonging to eachof the G groups are multiplexed by DFDM; reference signals of the UEsbelonging to a corresponding one of the G groups are multiplexed by CDMin a reference resource having the total bandwidth of the controlsignals for the UEs belonging to the corresponding one of the G groups.

According to the present embodiment, in the case where control signalshave three types of transmission bandwidths (a bandwidth fortransmitting Ack/Nack only, a bandwidth for transmitting CQI only, and abandwidth for transmitting both of Ack/Nack and CQI), a UE transmittingAck/Nack only, a UE transmitting CQI only, and a UE transmitting both ofAck/Nack and CQI are multiplexed by LFDM and DFDM in a bandwidthobtained by grouping as described above.

6.1) Example 5

FIG. 13 is a diagram showing an example of the allocation of resourcesfor control and reference signals according to the third exemplaryembodiment of the present invention. Here, it is assumed that controland reference signals are multiplexed by time division multiplexing(TDM), and that in each sub-frame, data and control signals aretransmitted in long blocks (LB) and reference signals are transmitted inshort blocks (SB), as shown in FIG. 1A for example.

In the present example, the total of a bandwidth used to transmitAck/Nack of two UEs and a bandwidth used to transmit CQI of two UEs, issupposed to be a unit bandwidth over which reference signals aremultiplexed by CDM. Specifically, referring to FIG. 13, a UE 2, whichtransmits Ack/Nack only, and a UE 4, which transmits CQI only, aremultiplexed by LFDM as in the second exemplary embodiment, and a controlsignal for a UE 1, which contains both of Ack/Nack and CQI and has thesame bandwidth as the total bandwidth of the LFDM control signals forthe UEs 2 and 4, is multiplexed with the LFDM control signals by DFDMwith a repetition factor of 2. Accordingly, with respect tocorresponding reference signals used for demodulation, the three UEs aremultiplexed by CDM over the entire bandwidth in which the controlsignals for the UEs 1, 2, and 4 are multiplexed by DFDM.

Similarly, a UE 3, which transmits Ack/Nack only, and a UE 5, whichtransmits CQI only, are multiplexed by LFDM, and the UEs 3 and 5 arefurther multiplexed with a UE 6, which transmits both of Ack/Nack andCQI, by DFDM with a repetition factor of 2. Accordingly, with respect toreference signals of the UEs 3, 5, and 6, the three UEs are multiplexedby CDM over the entire bandwidth in which their control signals aremultiplexed by DFDM.

According to the present example, even the reference signals of the UEs2 and 3, which transmit Ack/Nack only, are transmitted over a bandwidththat is twice as wide as the total bandwidth of Ack/Nack and CQI.Accordingly, it is possible to achieve a CAZAC sequence length that istwice as long as the length according to the example shown in FIG. 9.However, the number of the reference signals multiplexed by CDM islarger than in the second exemplary embodiment.

6.2) Example 6

FIG. 14 is a diagram showing another example of the allocation ofresources for control and reference signals according to the thirdexemplary embodiment of the present invention. Shown here is the casewhere, in a LTE's uplink frame format as shown in FIG. 3, controlsignals and data signals are multiplexed by frequency divisionmultiplexing (FDM), and their respective transmission bands arecompletely divided. In the band where control signals are transmitted,Ack/Nack and/or CQI are transmitted in long blocks, and referencesignals are transmitted in short blocks.

Referring to FIG. 14, in short blocks SB#1 and SB#2, reference signalsof UEs 1 to 6, which transmit control signals only, are appropriatelymultiplexed by CDM, using a bandwidth corresponding to Ack/Nack and CQIin double. Specifically, the UE 2, which transmits Ack/Nack only, andthe UE 4, which transmits CQI only, are multiplexed by LFDM, and theirLFDM control signals are further multiplexed by DFDM with a controlsignal for the UE 1, which contains both of Ack/Nack and CQI and has thesame bandwidth as the total bandwidth of the LFDM control signals.Accordingly, with respect to reference signals used to demodulate thesecontrol signals, the three UEs are multiplexed by CDM in the entire bandwhere the control signals for the UEs 1, 2, and 4 are multiplexed byDFDM. Control and reference signals of the UEs 3, 5, and 6 are similarlymultiplexed.

On the other hand, in the band where data signals are transmitted, datasignals are transmitted in long blocks, and reference signals aretransmitted in short blocks. Referring to FIG. 14, reference signals forUEs 7 and 8, which transmit data signals, individually occupy theirrespective bands in the short block SB#1, and are multiplexed by DFDMwith a reference signal for CQI measurement of a UE 9 in the short blockSB#2.

Note that although control and data signals are multiplexed by FDM inthe present example, the resource allocation of the present example issimilarly applicable in the case where control and data signals aremultiplexed by TDM.

6.3) Advantages

According to the third exemplary embodiment of the present invention,control signals for multiple UEs are multiplexed by LFDM. Further, LFDMcontrol signals having the same total bandwidth are multiplexed by DFDM.Their corresponding reference signals are multiplexed by CDM over theentire bandwidth in which the control signals are multiplexed by LFDMand DFDM. Thereby, the CAZAC sequence length can be increased. Moreover,since DFDM is used to multiplex control signals, the characteristics ofthe control signals can be enhanced by the effect of frequencydiversity, in comparison with the above-described second exemplaryembodiment.

Note that although the above-described embodiments are premised on theapplication to LTE, the application of the present invention is notlimited to LTE. The present invention can be applied to any systems ingeneral that use FDM as an access method.

7. Advantages of 2nd and 3rd Exemplary Embodiments

Tables 1 and 2 show the numbers of usable CAZAC sequences in the caseswhere control and data signals are multiplexed by TDM and by FDM. In thecase of TDM, the multiplexing scheme according to the second exemplaryembodiment is used. In the case of FDM, any one of the multiplexingschemes according to the second and third exemplary embodiments is used.Here, two options CQI size are assumed.

TABLE I Number of Number of Bandwidth subcarriers CAZAC usable of incontrol sequence CAZAC reference signal/LB length sequences signal (kHz)Conventional TDM 6/44/50 1/11/11 0/10/10 30/330/330 Example FDM 1/7/81/3/4 0/2/2 30/90/120 Present TDM 50 11 10 330 Invention FDM 16 7 6 210

TABLE II Number of Number of Bandwidth subcarriers CAZAC usable of incontrol sequence CAZAC reference signal/LB length sequences signal (kHz)Conventional TDM 6/30/36 1/7/9 0/6/6 30/210/270 Example FDM 1/5/6 1/2/30/1/2 30/60/90 Present TDM 36 9 6 270 Invention FDM 12 5 4 150

In the examples shown in Table 1, it is assumed that Acks/Nacks and/orCQIs for six UEs are multiplexed in a sub-frame within 5 MHz. In thiscase, six subcarriers are used for Ack/Nack, and 44 subcarriers are usedfor CQI.

In the examples shown in Table 2, it is assumed that Acks/Nacks and/orCQIs for eight UEs are multiplexed in a sub-frame within 5 MHz. In thiscase, six subcarriers are used for Ack/Nack, and 30 subcarriers are usedfor CQI.

Moreover, in these examples shown in Tables 1 and 2, one channel ofAck/Nack and one channel of CQI are grouped in the case of TDM, and twochannels of Ack/Nack and two channels of CQI are grouped in the case ofFDM. Additionally, in these tables, the values delimited with slashes(/) in each row and each column of “Conventional Example” show therespective results in the cases of “UE transmitting Ack/Nack only/UEtransmitting CQI only/UE transmitting both of Ack/Nack and CQI.”

It can be seen that by the application of the present invention, thenumbers of usable CAZAC sequences are increased from the numbersachieved in the conventional example. Taking account of the maximumnumber of UEs that can be multiplexed by CDM, six to ten CAZAC sequencescan be used in the case of TDM, and four to six CAZAC sequences can beused in the case of FDM.

8. Various Aspects

As described before, the object of the present invention is to provide amultiplexing method and a resource allocation method that can ensure thenumber of code sequences for reference signals used to demodulatecontrol signals.

According to the present invention, reference signals for a plurality ofmobile stations are multiplexed by CDM (code-division multiplexing) overthe same bandwidth as that of grouped control signals for the mobilestations. Resource allocation is performed by grouping together controlresources used for the control signals; and allocating reference signaleach corresponding to the control signals in a reference resource equalto the same bandwidth as that of the grouped control resources.

According to another aspect of the present invention, a multiplexingmethod includes: grouping together a control signal for each mobilestation; multiplexing grouped control signals by FDM (frequency divisionmultiplexing); and when the grouped control signals are associated witha plurality of mobile stations, multiplexing reference signals for theplurality of mobile stations by CDM over a same bandwidth as atransmission bandwidth of the grouped control signals.

According to still another aspect of the present invention, amultiplexing method includes: multiplexing control signals for N mobilestations by FDM in a control resource; grouping together control signalsfor M_(i) mobile stations (1≦M_(i)≦N, 1≦i≦I, M₁+M₂+ . . . +M_(I)=N) suchthat their bands are adjacent in frequency domain, to generate I groups(1≦I≦N); and multiplexing reference signals for the M_(i) mobilestations by CDM in a reference resource having a bandwidth equal to abandwidth of each of the I groups.

More specifically, CAZAC (Constant Amplitude Zero Auto-Correlation)sequence is used as the reference signal and a value of M_(i) isselected so as to satisfy a condition such that a bandwidth of groupedcontrol signals for the M_(i) mobile stations is not smaller than abandwidth corresponding to a predetermined reference sequence length.For example, considering the case of 3-sector/3-cell repetition system,9 CAZAC sequences are needed and therefore a reference signal length is11 at the minimum to ensure the 9 CAZAC sequences. Considering the caseof 3-sector/4-cell repetition system, 12 CAZAC sequences are needed andtherefore a reference signal length is 13 at the minimum to ensure the13 CAZAC sequences. Assuming that a reference signal is transmitted in ashort block SB (sub-carrier interval=30 kHz), the respectivetransmission bandwidths are 330 kHz and 390 kHz.

According to an exemplary embodiment of the present invention, each ofthe control signals has a bandwidth that is allocated depending on oneor more type of control information selected for each mobile stationfrom a plurality of types of control information having differentamounts of information. Among bandwidths each allocated to the mobilestations, the control signals for M_(i) mobile stations having the sametransmission bandwidth are multiplexed by Distributed FDM and thereference signals for the M_(i) mobile stations are multiplexed by CDMin a reference resource having a bandwidth equal to a bandwidth of eachof the I groups each composed of grouped control signals for the M_(i)mobile stations.

According to another exemplary embodiment of the present invention,control signals for M_(i) mobile stations (1≦M_(i)≦N, 1≦i≦I, M₁+M₂+ . .. +M_(I)=N) are multiplexed by Localized FDM regardless of bandwidthseach allocated to the mobile stations, to generate I groups (1≦I≦N);control signals in each of G groups ((1≦G≦I) are multiplexed byDistributed FDM, wherein the G groups are obtained by grouping ones ofthe I groups having a same bandwidth; and reference signals for mobilestations belonging to each of the G groups are multiplexed by CDM in areference resource having a bandwidth equal to a total bandwidth ofcontrol signals for the mobile stations belonging to a corresponding oneof the G groups.

Preferably, in a frame where a plurality of long blocks and short blocksare multiplexed by time division multiplexing, a control resource usedfor the control signals may be allocated long blocks and a referenceresource is allocated short blocks.

According to the present invention, reference signals of multiple UEsare multiplexed by CDM using the total bandwidth of grouped controlsignals for the multiple UEs. Thereby, even if a control signal having asmall transmission bandwidth (such as Ack/Nack, for example) istransmitted, the length of a CAZAC sequence used as a reference signalfor control signal demodulation can be made long. Thus, it is possibleto ensure the number of code sequences for reference signals used todemodulate control signals. Accordingly, in a cellular system forexample, it is possible to simplify the cell designing with respect touplink reference signals.

The present invention can be applied to mobile communications systemsemploying a scheme of transmitting control signals and correspondingreference signals, and systems including base and mobile stations.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Theabove-described exemplary embodiments are therefore to be considered inall respects as illustrative and not restrictive, the scope of theinvention being indicated by the appended claims rather than by theforegoing description, and all changes which come within the meaning andrange of equivalency of the claims are therefore intended to be embracedtherein.

The invention claimed is:
 1. A first mobile station comprising: aFourier transform unit configured to Fourier transform a first controlsignal; a mapping unit configured to map the Fourier transformed firstcontrol signal such that the first control signal and a second controlsignal are multiplexed within a first transmission bandwidth, the secondcontrol signal being transmitted by a second mobile station to a basestation; an inverse Fourier transform unit configured to inverse Fouriertransform the mapped first control signal; a transmitter configured totransmit the inverse Fourier transformed first control signal to thebase station in a first transmission interval; and a reference signalgeneration unit configured to generate a first reference signal sequencehaving a sequence length corresponding to an amount of all subcarriersincluded in the first transmission bandwidth; wherein the mapping unitmaps the generated first reference signal sequence such that the firstreference signal sequence is code multiplexed with a second referencesignal sequence, which is transmitted by the second mobile station tothe base station, within the first transmission bandwidth, the secondreference signal sequence having the same sequence length as the firstreference signal sequence; and the transmitter transmits the mappedfirst reference signal to the base station in a second transmissioninterval.
 2. The first mobile station according to the claim 1, whereina third control signal, which is transmitted by a third mobile stationin the first transmission interval, and a fourth control signal, whichis transmitted by a fourth mobile station in the first transmissioninterval, are multiplexed within a second transmission bandwidth, and athird reference signal sequence, which is transmitted by the thirdmobile station to the base station in the second transmission interval,is code multiplexed with a fourth reference signal sequence, which istransmitted by the fourth mobile station to the base station in thesecond transmission interval, within the second transmission bandwidth,wherein the second transmission bandwidth has a same size as the firsttransmission bandwidth and the third reference signal sequence and thefourth reference signal sequence have the same sequence length as thefirst reference signal sequence.
 3. The first mobile station accordingto the claim 2 wherein, the first reference signal sequence, the secondreference signal sequence, the third reference signal sequence and thefourth reference signal sequence are Constant Amplitude ZeroAuto-Correlation (CAZAC) sequences.
 4. A method comprising: Fouriertransforming a first control signal transmitted by a first mobilestation; mapping the Fourier transformed first control signal such thatthe first control signal and a second control signal are multiplexedwithin a first transmission bandwidth, the second control signal beingtransmitted by a second mobile station to a base station; inverseFourier transforming the mapped first control signal; transmitting theinverse Fourier transformed first control signal to the base station ina first transmission interval; generating a first reference signalsequence having a sequence length corresponding to an amount of allsubcarriers included in the first transmission bandwidth; mapping thegenerated first reference signal sequence such that the first referencesignal sequence is code multiplexed with a second reference signalsequence, which is transmitted by the second mobile station to the basestation, within the first transmission bandwidth, the second referencesignal sequence having the same sequence length as the first referencesignal sequence; and transmitting the mapped first reference signal tothe base station in a second transmission interval.
 5. The methodaccording to the claim 4 wherein, a third control signal, which istransmitted by a third mobile station in the first transmissioninterval, and a fourth control signal, which is transmitted by a fourthmobile station in the first transmission interval, are multiplexedwithin a second transmission bandwidth, and a third reference signalsequence, which is transmitted by the third mobile station to the basestation in the second transmission interval, is code multiplexed with afourth reference signal sequence, which is transmitted by the fourthmobile station to the base station in the second transmission interval,within the second transmission bandwidth, wherein the secondtransmission bandwidth has a same size as the first transmissionbandwidth and the third reference signal sequence and the fourthreference signal sequence have the same sequence length as the firstreference signal sequence.
 6. The method according to the claim 5wherein, the first reference signal sequence, the second referencesignal sequence, the third reference signal sequence and the fourthreference signal sequence are Constant Amplitude Zero Auto-Correlation(CAZAC) sequences.